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  • Side effects or symptoms after vaccination


Side effects or symptoms after vaccination

COVID-19 vaccines can cause side effects, but they are mostly mild or moderate, and pass after a few days. For some, the symptoms will be more severe. Side effects from the vaccines are being closely monitored.

jente med tre røde sirkler plassert på skuldre og ved hodet for å illustrere mulige bivirkninger etter vaksinasjon
Illustrasjon: FHI

COVID-19 vaccines can cause side effects, but they are mostly mild or moderate, and pass after a few days. For some, the symptoms will be more severe. Side effects from the vaccines are being closely monitored.

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The coronavirus vaccines may cause side effects in many of those vaccinated, but they are mostly mild / moderate and pass after a few days. For some, the symptoms may be more severe. The mRNA vaccines appear to cause more of the common side effects than other vaccines. Nuvaxovid generally has slightly milder side effects with a shorter duration than the mRNA vaccines.

The side effects after all three coronavirus vaccines usually occur during the first 1-2 days after vaccination. Common side effects are pain and swelling at the injection site, fatigue, headache, muscle aches, chills, joint pain and fever. Allergic reactions occur in some people. There is good knowledge about common side effects after vaccination, but rare side effects cannot be ruled out.

Among the rarer side effects reported from mRNA vaccines and Nuvaxovid are inflammation of the heart muscle (myocarditis) and inflammation of the pericardium (pericarditis). The condition most often occurs among adolescents and young adults. It also seems to occur more often with the use of Spikevax (Moderna) than with Comirnaty (BioNTech/Pfizer). When offering coronavirus vaccines to people under 30 years, the Norwegian Institute of Public Health (NIPH) recommends the use of Comirnaty for both men and women.

Among those who experience myocarditis and pericarditis recover within one month. The condition causes chest pain, wheezing, palpitations and fever. In case of such symptoms, consult a doctor for a medical examination. Norwegian cardiologists consider that COVID-19 disease can cause more serious heart effects in some people than after the vaccine, and that this rare side effect should not prevent adolescents from being offered the vaccine.

Cases of menstrual disorders have been reported following coronavirus vaccination. The NIPH uses population studies to gain answers as to whether there may be a connection between the coronavirus vaccines and these symptoms. The initial results from these studies in young women showed that more reported heavier menstrual bleeding after being vaccinated with the COVID-19 vaccine, and heavy menstrual bleeding has been subsequently listed as a possible side effect in the product information for the mRNA vaccines. Monitoring is still ongoing. Read more about how side effect signals are followed up in the text box below.

When large parts of the population are vaccinated, many will experience common diseases and complaints in the period after vaccination. Symptoms that occur in the period after vaccination are not always due to the vaccine. Vaccine side effects can sometimes be difficult to distinguish from symptoms of infections or other diseases. If you experience unexpected, severe or prolonged symptoms after vaccination, you should contact your doctor or other healthcare professional for assessment and advice. Healthcare professionals have a duty to report serious or unknown reactions that they suspect are due to a vaccine. You can also send a message via the form via helsenorge.no.

Follow-up of side effects

When vaccines are developed, the goal is always for vaccines to give the best possible effect with the fewest possible side effects. Even if the new vaccines are tested thoroughly, rare side effects cannot be ruled out. Some side effects are only discovered when vaccines are in wider use and have been given to many more people and to more varied groups than in the studies.

After the vaccines are in use, the Norwegian Medicines Agency, together with the NIPH, will monitor closely whether any unexpected side effects arise. There is also extensive international collaboration with the other countries that use the same vaccines. In addition, the vaccine manufacturers are required to conduct new systematic safety studies.

What happens to the notifications about side effects?

The NIPH processes reports of suspected side effects from healthcare personnel. The notifications are entered in the ADR Registry at the Norwegian Medicines Agency.

The Norwegian Medicines Agency publishes regular reports with an overview of reports of suspected adverse reactions after vaccination in Norway.

Notifications from healthcare professionals are thoroughly assessed to find out if the incident may be due to the vaccine, or if it happened at the same time as vaccination. It is important to be aware that events that coincide in time are not necessarily due to vaccination. Therefore, a medical examination is recommended to check for other explanations for the events. In some cases, it can be difficult to conclude whether an event is due to a vaccine or coincidence based on one or a few single events. 

Long-term effects and delayed side effects 

More than 12 million doses have been administered in Norway, and almost 13 billion doses globally. This provides good insight and knowledge about side effects after coronavirus vaccination.

What is the difference between long-term side effects and delayed side effects?

It is important to distinguish between long-term side effects and delayed side effects.

  • Long-term side effects persist (longer than 3 months)
  • Delayed side effects only appear more than six weeks after vaccination.

Unusual with side effects later than two weeks after vaccination

For coronavirus vaccines and other vaccines, side effects usually occur in the first few days and within the first two weeks after vaccination. Side effects occurring more than 6 weeks after vaccination are referred to as delayed or long-term side effects. However, it is very unusual for reactions to occur so long after vaccines are given.

This knowledge comes from wide experience from the use of many different vaccines over several decades. Every year since 1952, hundreds of thousands of vaccine doses have been administered through the Norwegian childhood immunisation programme. In addition, a large proportion of the population receives an annual influenza vaccine, and adults are recommended to have regular booster doses of several vaccines, e.g. travel vaccines.

Delayed side effects after vaccination in Norway

Of all the vaccines and vaccine types given in Norway, one vaccine was registered with a serious side effect more than 6 weeks after vaccination. Pandemrix was offered during the swine influenza pandemic in 2009/2010 where some children and adolescents developed narcolepsy after vaccination. 700,000 people under the age of 30 were vaccinated with Pandemrix and 56 were diagnosed with narcolepsy. 60,000 in the same age group were registered as having influenza disease and 16 of the unvaccinated group also developed narcolepsy.

Clinical study participants monitored for minimum of one year

When new vaccines are developed, large clinical trials are conducted with many thousands of people, with strict international requirements. Clinical studies give us good knowledge about the most common side effects.

Vaccine manufacturers are also required to follow up the study participants for a minimum of one year after vaccination to give the global community more knowledge about the effect of the vaccine and to detect any long-term side effects.

Suspected new side effects are called signals

Suspicion about new side effects can come from different directions - from those who have received the vaccine, from researchers, or from healthcare professionals. This is picked up either by researchers publishing peer-reviewed medical journals or by people and healthcare professionals reporting suspected side effects, known as spontaneous reporting.

The Norwegian Medicines Agency monitors side effect signals in Norway, and the NIPH assists in the work.

An extensive international collaboration identifies potential new side effects and follows up any signals received. The signals must be investigated before they can be assessed for a possible causal association with vaccination or not, and this must be both thorough and timely. As a rule, little will be known about what triggers a possible new side effect, when and how often they occur, and whether some groups are more at risk of side effects than others. This is something that the most important studies try to identify.

It is very important to be able to compare the incidence of a possible side effect among those who have and who have not received vaccines. However, since many people in Norway have now received a coronavirus vaccine, it is not so easy to compare vaccinated against unvaccinated. Good health registry data and studies are essential to be able to compare the common incidence of various diseases in the population before and after coronavirus vaccination began.

Good health registries and collaboration allow quick response

Access to reliable health data in the NIPH's emergency preparedness registry Beredt C19 has given us new opportunities to study signals about side effects, and monitor changes in the incidence of various diseases in the population. If many cases of a particular condition are reported after vaccination, it will be possible to quickly investigate using health registry data whether the number of cases of the condition is higher among those who have received the vaccine than usual.

The NIPH collaborates with other Nordic countries on studies of signals in order to obtain a larger, common statistical basis. In this way, the possibility of detecting any changes in the occurrence of rare side effects is increased. Compilation of data from national health registries in several Nordic countries has been important in the investigation of rare suspected side effects after coronavirus vaccination.

Stopped AstraZeneca vaccine 

An example of this working well was when vaccination with Vaxzevria (AstraZeneca) was suspended in March 2021. At that time, health registry data compiled from Norway and Denmark showed an increased risk of a serious and unusual blood clot condition in the brains of vaccinated people compared to those who were not vaccinated. Vaxzevria was removed from the Norwegian coronavirus immunisation programme in May 2021 as a result of these side effects.

People under 30 years are recommended Comirnaty

Another example is the increased risk of heart inflammation after COVID-19 disease. The first signals that the mRNA vaccines could cause inflammatory conditions in the heart (myocarditis and pericarditis) came in April 2021. After reviewing the adverse reaction data, myocarditis and pericarditis were added as rare side effects after the mRNA vaccines Comirnaty (BioNTech / Pfizer) and Spikevax (Moderna), and the vaccination recommendations were changed.

Compilation of health registry data from Norway, Sweden and Denmark showed a higher incidence of these relatively rare inflammatory conditions among vaccinated than among unvaccinated people. The risk is highest after the second dose for those under 30, especially men, and higher after vaccination with Spikevax than after Comirnaty. As a precautionary principle, we recommended that both women and men under the age of 30 should choose Comirnaty over Spikevax.

Large-scale population studies provide important insights

In Norway, signals of milder side effects that do not necessarily lead to people contacting the health service are also monitored through NIPH's large ongoing population studies (cohort studies).

When the signal about menstrual disorders appeared in the spontaneous reporting system of the Norwegian Medicines Agency, questions about menstruation were quickly included in these studies for female participants. The first results from the studies show that coronavirus vaccination can affect menstruation in young women 18-30 years. Based on this, the NIPH issued advice to women who have experienced this:

After a review of available data, including reported side effect reports from European countries, clinical trials and publications, heavy menstrual bleeding was listed as a possible side effect with an unknown frequency in the summary of product characteristics (SmPC) and package insert of Comirnaty (BioNTech/Pfizer) and Spikevax (Moderna) in October 2022. Analyses are still ongoing to investigate whether there is a connection between COVID-19 vaccination and menstrual disorders in other age groups. Data have also been collected on other symptoms, including persistent headaches, fatigue and worsening of chronic diseases. Analyses of the data collected in the cohort studies are ongoing, and it is too early to comment on a possible connection with vaccination.

Number of adverse reaction reports will continue to increase

With such a large proportion of vaccinated people in the population, reports of symptoms or conditions with a suspected association with the vaccine will be received for a long time to come. This is a natural consequence of the notification system.

Any suspected link between an incident and vaccination should be reported in order to identify possible side effects that can then be investigated further. Reports of suspected side effects provide useful knowledge about the vaccines and are important to provide sound vaccination advice. The aim of a vaccine is always to give the best possible effect with the fewest possible side effects.

The NIPH considers that the benefit of the vaccines we use in Norway (protection against severe COVID-19 disease course) is much greater than the risk of serious vaccine side effects. Our assessments are based on the latest available knowledge about the vaccines and about COVID-19 disease.

The health authorities continue to monitor the situation closely both in Norway and the rest of the world. Even after thorough studies prior to approval, we can never guarantee that rare side effects will not occur when vaccines are used on large population groups. Any new signals or suspected side effects that appear that may be related to the vaccines will be thoroughly investigated.


06.12.2022: This article is based on text from a section in the coronavirus vaccine article about side effects combined with text from a news article about long-term effects